Danny O'Connor has only one place in his native Larne where he can buy a drink to celebrate the thirtieth birthday of the Social Democratic and Labour Party tomorrow. The party's first ever Assembly member for loyalist-dominated East Antrim will have to confine himself to the local Catholic parish hall if he wants to uncork a bottle and toast the SDLP's founding fathers.

For Catholics in Larne, the port town which has witnessed an upsurge in sectarian attacks over the past fortnight, do not drink in the town at night for fear of being beaten up, or even killed, by loyalist gangs. To them, the area's pubs and clubs are no-go areas.

O'Connor himself has been at the sharp end of loyalist aggression since he was first elected to the Northern Ireland Assembly in 1998. His home has been attacked 12 times since the Good Friday Agreement was signed, and last week his brother's house was petrol bombed.

Yet this burly 35-year-old former security guard personifies the SDLP's best strategy to preserve its status as the principal nationalist party of Northern Ireland in face of a formidable threat from Sinn Fein.

His working-class roots challenge the stereotype of the SDLP simply being the party of the Catholic middles classes - teachers, solicitors and doctors. Elected to a constituency with an overwhelming Protestant majority, east of the river Bann, his success gives his party some hope that it can keep the IRA's political wing at bay. O'Connor has attracted the first preference votes of former Alliance Party voters and even second and third preference transfers from pro-Agreement Ulster Unionists - something Sinn Fein finds impossible to achieve outside the nationalist electorate.

The SDLP Assemblyman's office is a monument to the bigotry that blights Larne. The town has strong historical ties to hardline loyalism dating back to 1912, when the original Ulster Volunteer Force landed 30,000 rifles from the Clyde valley to arm people willing violently to resist Home Rule in Ireland. The windows of the office, above butchers' shop in Main Street, are bullet proof. There are scrapes and marks on the panes from the countless bricks, bottles and ball bearings fired at the SDLP base.

Inside last Friday afternoon O'Connor was counselling nervous Catholic families whose homes were petrol bombed last week during an orgy of sectarian intimidation across the town organised by the Ulster Defence Association.

Under siege from extreme loyalists, O'Connor takes comfort from the framed photograph on the wall of the American civil rights leader, Martin Luther King , one of his greatest heroes. His other hero is the SDLP leader, John Hume.

'There are two reasons why I joined the party seven years ago, he said. 'I used to work as a security guard at Shorts [aircraft factory] and I remember the day that loyalists shot up a minibus full of contract workers who were painting and decorating at the plant. These were guys I used to let into the factory in east Belfast every morning and say hello or good morning to. And then, when that gun attack happened, one of them was dead, wrapped in a blanket that barely covered him. The others were badly injured.

'I thought something should be done to stop this madness.'

The shooting happened in 1993, when Hume was talking to Sinn Fein's Gerry Adams in an attempt to persuade republicans to give up violence.

'John was coming under considerable pressure and criticism but I will never forget watching the relatives of the victims of the Greysteel massacre coming over to him at the funerals and telling him he had their full support to keep on talking. I remember Hume breaking down in tears and that's when I knew I had to join the party,' he said.

Like many SDLP representatives living in mainly loyalist areas, O'Connor paid the price for entering politics. Some of the party's early leaders were victims of both loyalist and republican intimidation. Austin Currie, now a Fine Gael TD in Dublin, suffered attacks from the UVF and the IRA. Loyalists bombed Seamus Mallon's home. Former leader Gerry Fitt had to force an IRA-inspired mob out of his house at gunpoint after they broke into his home threatening him and his family. As he waved his legally-held gun at the intruders, one of them shouted: 'Look, he's a coward, he's got a gun.' Worst of all Lord Fitt's friend Senator Paddy Wilson and his friend Irene Andrews were stabbed to death in a frenzied knife attack.

O'Connor accepted the risks of being a nationalist representative in a loyalist stronghold. 'The first cases I dealt with were Catholic constituents being burnt out of their homes. The people I represent are under attack and that means I have to stand firm and keep going.'

He blames the East Antrim UDA for orchestrating most of the violence directed against him, his family and his constituents. The RUC have told him he is on a loyalist death list. Yet he has founded the first branch of the SDLP in Larne and predicts that the party will elect more councillors to the local borough council next May.

West of the Bann, the party is fighting a rearguard struggle against a highly organised, disciplined and well-financed Sinn Fein. In Westminster constituencies such as West Tyrone, it is Sinn Fein rather than the SDLP which is seen as the main challenger to the sitting Unionist MPs. But east of the river dividing Northern Ireland, John Hume's party is clearly making inroads into the Alliance vote and gaining fresh support from the new Catholic middle-class emerging in areas that were once 100 per cent unionist.

Optimistically, O'Connor dismisses the prophets of doom who predict the demise of the SDLP and the further rise of Sinn Fein.

'The Agreement was pure SDLP politics in practice, compromise and common sense. They've been arguing for a settlement like this for 30 years long before Sinn Fein started to get into real politics. Unlike Sinn Fein I can reach out to others beyond nationalism, to people from Unionist and Alliance backgrounds that voted for the Agreement. All republican violence achieved over 25 years was to drive people further apart.'